Petroleum Geology of the Parshall Field Area, Mountrail County, North DakotaAndrea Simenson and Stephen A. Sonnenberg

1,2 1

1

2

Department of Geology, Colorado School of Mines, Golden, COThe Discovery Group Inc, Denver, CO

ABSTRACT

The Parshall Field of the Williston Basin was discovered in 2006 byEOG Resources. This Devonian-Mississippian middle BakkenFormation resource play covers some 40 townships in MountrailCounty, North Dakota and is still expanding. The development ofhorizontal drilling and modern fract techniques has made this fieldpossible.

The Bakken Formation in the field area consists of three members:(1) upper shale, (2) middle dolomitic sandstone, (3) lower shale. Thetotal Bakken interval ranges in thickness from 80 to 130 ft over thefield area. The upper shale is dark-brown to black organic richmudstone and ranges in thickness from 10 to 18 ft over the field area.The middle member ranges in lithology from bioturbated,argillaceous, calcareous very fine grained sandstones to cross-bedded fine to very fine-grained sandstone to very fine-grainedsandstone with cm scale shale laminations. The middle memberranges in thickness from 30 to 70 ft. The lower shale member is alsoa dark-brown to black organic rich mudstone and ranges in thicknessfrom 20 to 45 ft.

The main reservoir in the Parshall Field is the middle member whichhas low matrix porosity and permeability and is found at depths of9000 to 10500 ft. The middle Bakken porosities range from 2 to 12%and permeabilities average 0.02 mD. Some key factors thatcontribute to the success of this play include good stratigraphictrapping conditions, generation of hydrocarbons from the organic richmudstones, and fractures.

Facies F – Patterned pyritic dolostones andcalcitic, whole fossil, dolo-to limewackestones: fossil-rich beds

Fossil beds may represent storm depositsAbsence of waves and currents,

suspension deposition

�

�

Facies E – Thin-bedded dolo-mud/wackestone

Can be rhythmically beddedOffshore settingRhythmically interlaminated sandstone and

muddy siltstone may represent tidalprocesses

Thin sandstone beds interpreted astempesites strongly reworked by biogenicaction

�

�

�

�

Facies D – Highest energy, coarsest grainedalternating cross-bedded bioclast, very finegrained sandstone

Interpreted as having been deposited in ahigh-energy region: channel fill to shoal�

Facies C – Rhythmic, varve-like, mm to cmlaminated, well sorted, very fine grainedsandstone and siltstone with calcite cement,hummocks and wave ripples

Rhythmically interlaminated sandstone andmuddy siltstone may represent tidal processes�

Facies B – Bioturbated, argillaceous,calcareous, poorly sorted, very fine grainedsandstone/siltstone with

Open-marine, below storm wave base,reworking by deposit feeding ichnofauna

helminthopsis/sclarituba

�

Facies A – Intraclastic-skeletal limewackestone, 1-4 ft thick

Absence of waves and currents, suspensiondeposition, deposit-feeder traces

High index of bioturbation and commonshell fragments

�

�

Upper Bakken Shale - Black, massive tolocally parallel-laminated shale

Lower Bakken Shale - Black, massive tolocally parallel-laminated shale

Late Devonian - Early Mississippian Bakken Petroleum Systemincluding the Lower Lodgepole Formation, Bakken Formation,and the Upper Three Forks Formation.

Late Devonian - Early Mississippian black shalespaleogeography distribution map. The BakkenFormation is located in the northern United States andsouthern Canada.

Location of the Parshall Field in Mountrail CountyNorth Dakota. The study area is highlighted in red.

Selected wells used in the study. Wells were chosenbased on penetration of the entire Bakken Formation,well logs availability, and core availability.

Unconventional, Continuous Tight OilAccumulations

Prevasive petroleum saturationMature source rockAbnormally pressureGenerally lacks down-dip waterUp-dip water saturationLow porosity and permeability reservoirsEnhanced by fracturing and partings

�

�

�

�

�

�

�

From LeFever, 2008

From Smith and Bustin, 1996 Facies based on work done by Cantor et al, 2009

GR RES GR

DENNEU